WASHINGTON (Reuters) - An anti-smoking drug sold by Pfizer
Inc will carry more prominent warnings that patients be
monitored for unusual activity including agitation, depression
and suicidal behavior, the company said on Friday.

The world's largest drugmaker said it worked with the U.S.
Food and Drug Administration to update an earlier label change
enacted last year for its drug Chantix.

The new label offers a similar recommendation to monitor
patients, but the language is more prominently located to
better get the attention of doctors, Pfizer officials said.

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"Basically there was an evolution of thinking of where it
would be best to place (the advice) on the label," Pfizer Vice
President for Medical Affairs Ponni Subbiah said in an
interview.

New York-based Pfizer said no causal relationship has been
established between the drug and the behaviors, but in some
cases, an association could not be ruled out.

The drug has been prescribed to 4 million people in the
United States since approval in 2006, according to Pfizer.

The revised section is not a "black box," a warning
reserved for what the FDA deems the most dangerous potential
adverse events.

It directs doctors to observe patients on Chantix for
"serious neuropsychiatric symptoms, including changes in
behavior, agitation, depressed mood, suicidal ideation and
suicidal behavior," according to Pfizer.

In November, the FDA issued an early warning after
receiving reports of suicidal thoughts and behavior, and at
least one death, potentially linked to the medication.

The FDA has been analyzing reports of erratic and
aggressive behavior, and suicidal thoughts and behavior in
patients taking the prescription drug, known generically as
varenicline.

Pfizer said reports may be complicated by patients with
pre-existing psychiatric illness and by symptoms of nicotine
withdrawal.

The November FDA assessment revealed "that many of the
cases reflect new-onset of depressed mood, suicidal ideation
(thoughts) and changes in emotion and behavior within days to
weeks" of starting treatment.

Pfizer reported third-quarter sales of $241 million in the
for Chantix, up from $33 million a year earlier. Although not
huge by Pfizer standards, some analysts are hoping the drug can
help bolster profits as other major drugs face generic
competition.